The present invention relates to antiperspirant compositions for application to human skin, and to the preparation and use of such compositions.
A wide variety of cosmetic compositions for application to human skin make use of a structured liquid carrier to deliver an active material to the surface of the skin, including in particular antiperspirant or deodorant compositions which are widely used in order to enable their users to avoid or minimise wet patches on their skin, especially in axillary regions or to control or prevent the emission of malodours, which could otherwise arise when the user perspires.
Antiperspirant or deodorant formulations have been provided with a range of different product forms. One of these is a so-called xe2x80x9cstickxe2x80x9d which is usually a bar of an apparently firm solid material held within a dispensing container and which retains its structural integrity and shape whilst being applied. When a portion of the stick is drawn across the skin surface, a film of the stick composition is transferred to the skin surface. Although the stick has the appearance of a solid article capable of retaining its own shape for a period of time, the material often has a structured liquid phase so that a film of the composition is readily transferred from the stick to another surface upon contact.
Although structuring is a term that has often been employed in respect of materials which structure a carrier liquid, various other terms have been employed alternatively, including solidifying and gelling.
Antiperspirant sticks can be divided into three categories. Suspension sticks contain a particulate antiperspirant active material suspended in a structured carrier liquid phase which often is anhydrous and/or in many instances may be water-immiscible. Emulsion sticks normally have a hydrophilic phase, commonly containing the antiperspirant active in solution, this phase forming an emulsion with a second, more hydrophobic, liquid phase. The continuous phase of the emulsion is structured. Solution sticks typically have the antiperspirant active dissolved in a structured liquid phase which is polar and may comprise a polar organic solvent, which is often water-miscible, and the polar phase can contain water.
There is substantial literature on structuring of antiperspirant or deodorant compositions.
Conventionally, many suspension sticks have been structured using naturally-occurring or synthetic waxy materials, in which term we include materials which resemble beeswax, in that they soften progressively with increase in temperature until they are fluid, generally by about 95xc2x0 C. Examples of wax-structured sticks are described in an article in Cosmetics and Toiletries, 1990, Vol 105, P75-78, in U.S. Pat. Nos. 5,169,626 and 4,725,432 and in many other publications, in some of which such materials are called solidifying agents.
More specifically, it has been common practice for suspension sticks to be structured or solidified by incorporating fatty alcohol into the composition, often accompanied by a smaller amount of castor wax. Sticks which are structured with fatty alcohol tend to leave visible white deposits on application to human skin; moreover the deposits can also transfer onto clothing when it comes into contact with the skin and the wearer can, for example, find white marks at the armhole of the sleeveless garment. Fatty alcohols are often regarded as coming within the general category of waxy materials, but we have observed that they are a more significant source of white deposits than various other waxy materials. Consumer tests have identified that such white marks are disliked by some consumers and indeed, at least in some countries a market has developed for antiperspirant products which leave little or no such apparent marks on application to the skin.
Patent literature has also proposed the preparation of a suspension composition that not only does not leave visible marks upon skin application, but additionally is clear. Thus, for example Vu et al in U.S. Pat. No. 5,384,117 disclose anhydrous antiperspirant compositions in which a particulate antiperspirant is suspended in a liquid carrier having a matched refractive index to within about 0.02 such that the resultant composition has a relative turbidity of less than 800 FTU. The text exemplified the use of a polyethylene-vinyl acetate copolymer (AC-400 from Allied Corp) as gelling agent to solidify compositions containing various aluminium chlorohydrates antiperspirants, but did not exemplify any other structurants. Even a polyethylene homopolymer that was mentioned as an alternative was not exemplified, though the inventor was under a duty to disclose the best mode of operating the invention. It will be recognised that the text provides no teaching to the skilled man as to how to identify an alternative to the polyethylene-vinyl acetate copolymer.
It would be desirable to find an alternative structurant to the polymers exemplified by Vu for several reasons. First, the polymer exemplified by Vu is not a particularly effective structurant for water-immiscible liquids. The instant inventors found that gels produced using 20 parts by weight of AC-400A to 80 parts by weight of water-immiscible liquid containing a significant fraction of silicone oils were rather soft rather than firm at ambient temperature, even though that is a high weight ratio of structurant to carrier liquid. Moreover the gels produced appeared to be opaque when the refractive indexes of the carrier liquids were similar to those in Vu""s Examples. Vu also discloses potential processing difficulties with polymer gellants, including the need to prevent the carrier fluid/gellant mixture exceeding its cloud point.
The difficulty of creating a clear suspension stick which employs a non-polymeric material can be seen from the fact that many readily available non-polymeric gellants render a water-immiscible liquid carrier opaque when it is solidified by them. Such agents include many of the waxes and similar materials to which reference has been made hereinabove.
The difficulty of obtaining clear solidified compositions is further compounded by the fact that antiperspirant actives tend to have a refractive index that is significantly higher than conventional silicone oils, including particularly volatile silicone oils, such as cyclomethicones that have a refractive index just below 1.4, or even those commercially available non-volatile polyphenylmethylsiloxane liquids such as Dow Corning DC-556 which have an intermediate refractive index of around 1.45. Such a low refractive index renders it difficult to obtain sufficiently close refractive index matching to permit the resultant suspension to be clear without some additional carrier being employed. This becomes a greater problem as the refractive index of the antiperspirant increases, for example when employing an activated aluminium chlorohydrate instead of an aluminium chlorohydrate. Moreover, the overall difficulty of selecting a liquid carrier is exacerbated at least in part because antiperspirant compositions are left in place on the skin for long periods between washing, often all day, so that the other properties of a prospective liquid carrier must be kept in mind as well.
The problem of refractive index matching of active and carrier is at its worst for aluminium-zirconium antiperspirants which have the highest refractive index of conventional aluminium-containing antiperspirant actives, if the producer wishes to avoid alkoxycinnamate compounds such as octylmethoxy cinnamate, that have known disadvantage characteristics for leave on skin product (such as an antiperspirant) of colour, irritancy and possible toxicity. The skilled man would be prejudiced against employing the compositions of Vu""s Examples 1 to 12 on account of the presence of at least 13.5% up to 72.3% by weight of an alkoxy cinnamate therein. The skilled man can also recognise that Vu""s polymer would cause a suspension of aluminium-zirconium antiperspirant in to be opaque, even if he matched exactly the refractive indexes of carrier and antiperspirant, in view of the low refractive index of the polymer. That explains the absence from Vu of any Examples employing simultaneously polymer and aluminium-zirconium antiperspirant.
In U.S. Pat. Nos. 5,455,026 and 5,492,691, Bahr et al disclosed the formation of clear antiperspirant gels. Bahr set out various criteria, including selection of the same refractive index (RI) range for the antiperspirant active and the blend of carrier fluids, the matching of those RIs and it was also essential to select 12-hydroxystearic acid (12-HSA) or a salt thereof as gelator. Translucent gels were obtained, in their Examples 2 and 3 by matching absolutely the RI of the disperse particulate antiperspirant and the carrier fluid. However, where there was even a small difference in RI between the particles and the carrier fluid, 0.014 as in Comparative Example 4, the resultant composition was no longer clear, demonstrating much higher turbidity (the maximum on the scale 1000, compared with 240 and 272 respectively.
Three problems remain compared with Bahr""s disclosure. How can clarity be improved even when the RI matching is not absolute? How can clarity be achieved in anhydrous stick formulations employing water-immiscible oils as carrier for a particulate antiperspirant which are solidified by structurants other than 12-HSA? This problem relates to both clarity of the composition and formation of a stick. It will be recognised that, as mentioned previously herein, the materials disclosed in U.S. Pat. No. 5,348,117 were found to form soft rather than firm antiperspirant compositions. Thirdly, how can clear formulations be obtained which are not restricted to the range of RIs described by Bahr?
The instant inventors have recognised that any alternative structurant that is employed with the intention of obtaining a clear solid suspended antiperspirant product would ideally not only be capable of being refractive-index matched with the remaining constituents of the composition, but also that it should be a relatively tolerant to a change in the matched refractive index of carrier and antiperspirant, because it is considerably more difficult to match the refractive indexes of three components very closely, compared with only two. This enables a wider window of refractive index matched antiperspirant/carrier liquid to be employed and to cater for variations in RI which can arise in formulations, for example due to temperature changes or small variations between batches of ingredients, a matter of practical significance in full-scale manufacture.
Bahr discloses the suspension of a particulate antiperspirant salt having an RI of 1.510 or 1.514 and an undefined particle size distribution suspended in a carrier oil blend having an RI completely matched to the RI of the antiperspirant salt and gelled using solely 12-HSA. Such a combination is manifestly not within the present invention.
Objects of the present invention
It is an object of the present invention to ameliorate or overcome one or more of the problems identified hereinabove, for example on or more of the problems relative to the disclosure in U.S. Pat. Nos. 5,455,026/5,492,691 or to the disclosure in U.S. Pat. No. 5,348,117.
It is an object of the present invention to provide structured solid antiperspirant compositions, which demonstrate clarity, but which do not employ polymer structurants. A further object of some embodiments of the invention is to provide solid suspension aluminium-zirconium antiperspirant compositions of improved clarity.
When the instant inventors employed a particular class of structurants which they had found to be capable of providing the above-mentioned desirable wider RI window, they found that the particle size of the antiperspirant salt has a substantial and significant impact upon the clarity of the resultant suspension. Intuitively, it would be expected that smaller particles ought to be beneficial, but the situation in the real world is more complicated than that, and indeed, to at least some extent, is contrary to intuition. It will be recognised that Bahr in his US patents was silent concerning the particle size distribution of antiperspirant salts and manifestly was not aware of its potential significance.
Various structurants for water-immiscible oils as carrier fluids for suspended particulate antiperspirant salts have been disclosed in U.S. Pat. Nos. 6,231,841, 6,248,312, 6,251,377, 6,410,001, 6,410,003, and 6,458,344. None of said specifications disclose the instant invention.
Applicants have now found that clear solid suspension antiperspirant compositions can be obtained by employing together a selected class of carrier liquids, a selected class of structurants and particulate antiperspirant materials which satisfy a specified criterion.
Broadly, in a first aspect of the present invention, there is provided a clear anhydrous solid antiperspirant composition comprising from 0.5 to 50% by weight of a particulate antiperspirant salt suspended in a water-immiscible liquid carrier that is solidified by an effective amount of a structurant characterised in that:-
i) the particulate antiperspirant contains less than 50% by weight of particles having a diameter of up to 10 xcexcm and a refractive index of from 1.49 to 1.57 at 22xc2x0 C.,
ii) at least 50% by weight of the carrier liquid is selected from liquid non-volatile silicone oils and liquid alkyl-aryl esters
ii) not more than 25% by weight of the carrier liquid comprises a volatile silicone oil,
iv) the carrier liquid and the antiperspirant have refractive indexes which differ by no more than 0.02 at 22  C. and
v) the structurant comprises a fibre-forming non-polymeric structurant.
Herein, the term xe2x80x9cclearxe2x80x9d in respect of antiperspirant compositions indicates that at least 0.5% of light having a wavelength of 580nm at 22xc2x0 C is transmitted through a lcm sample.
A composition of this invention will generally be marketed in a container by means of which it can be applied at time of use. This container may be of conventional type.
By production of the composition in accordance with the criteria of the present invention, it is possible to obtain anhydrous antiperspirant suspension sticks which exhibit improved clarity compared with corresponding compositions in which, for example, the antiperspirant salt has a similar mean particle size but a different particle size distribution, and in particular when RI matching is not complete.
A second aspect of the invention therefore provides an antiperspirant product comprising a dispensing container having an aperture for delivery of the contents of the container, means for urging the contents of the container through the said aperture, and a composition of the first aspect of the invention in the container.
Means for urging the contents of the container to the said aperture or apertures, for flow through them, may be moving parts operable by the user or an orifice in the container opposite said aperture providing digital access. If desired, the container may itself be made from a clear material, possibly tinted, so that a consumer may recognise in pack that the composition is clear.
The compositions of this invention can be produced by conventional processes for making antiperspirant suspension solids.
Thus, according to a third aspect of the present invention there is provided a process for the production of a cosmetic composition comprising the steps of:
ai) incorporating into a water-immiscible liquid carrier a structurant which is one or more structurant compounds as defined in the composition of the first aspect,
a2) mixing the liquid carrier with a particulate antiperspirant active as described in the first aspect,
a3) heating the liquid carrier or a mixture containing it to an elevated temperature at which the structurant is dissolved or dispersed in the water-immiscible liquid carrier, steps al) a2) and a3) being conducted in any order followed by:
b1) introducing the mixture into a mould which preferably is a dispensing container, and then
cl) cooling or permitting the mixture to cool to a temperature at which-the liquid carrier is solidified.
According to the fourth aspect, there is provided a cosmetic method for preventing or reducing perspiration or odour formation on human skin comprising topically applying to the skin a composition comprising an antiperspirant active, a water-immiscible liquid carrier and,a structurant compound as described above in the first aspect.